Multibeam radar system

ABSTRACT

A multibeam radar system includes a multibeam radar module having n (n is a natural number of at least 3) transmitting/receiving channels for transmitting high-frequency signals and receiving echo signals, and a radar circuit for detecting a distance up to an object which produces the echo signals and/or a relative speed of the object from a relationship between the high-frequency signals and the echo signals in the transmitting/receiving channels. The radar circuit includes a channel controller for selecting sets of m (m is a natural number smaller than n) adjacent transmitting/receiving channels sequentially to transmit the high-frequency signals and receive the echo signals in a high-azimuth-resolution mode. The channel controller may also select the transmitting/receiving channels sequentially one by one to transmit the high-frequency signals and receive the echo signals in a low-azimuth-resolution mode.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multibeam radar system for use as adistance/speed detector in a collision alarm system on motor vehicles,and more particularly to a multibeam radar antenna and a multibeam radarmodule for radiating a plurality of radar beams in respective differentdirections with adjacent ones of the radar beams overlapping each other.

2. Description of the Prior Art

FM millimeter-wave radar devices for use as distance/speed detectors incollision alarm systems on motor vehicles are known from "Radartechnology" published by the Society of Electronic InformationCommunications. The known FM millimeter-wave radar devices radiate asignal whose frequency increases or decreases in a triangular wavepattern with time forwardly of the motor vehicle and receive an echosignal reflected by another motor vehicle running ahead. The receivedecho signal is mixed with the transmitted signal, generating a beatsignal. The distance up to the motor vehicle running ahead and the speedthereof are detected from the frequency of the beat signal.

For an FM radar system to be used as an automobile radar system, the FMradar system as installed on a motor vehicle running along a lane isrequired to detect a distance highly accurately within a range of 100 mand also to scan a road horizontally with high-frequency beams formonitoring motor vehicles running along left and right lanes in front ofits own motor vehicle. This is because it is possible for any one of themotor vehicles running ahead along the left and right lanes to enter thelane of its own motor vehicle, and when one of the motor vehicles entersthe lane, the speed of the motor vehicle equipped with the FM radarsystem has to be reduced to avoid collision.

Radar systems or apparatus for monitoring horizontal objects in front ofa motor vehicle are disclosed in U.S. Pat. Nos. 5,008,678 and 5,486,832.

The radar system disclosed in U.S. Pat. No. 5,008,678 employs planarmicrostrip Butler matrixes for electronically scanning radar beams.Because of the planar microstrip Butler matrixes, however, the disclosedradar system is relatively expensive to manufacture. It is importantthat radar systems for use as radar sensors on motor vehicles be reducedin cost as they also find applications in radar automatic cruise controlsystems (ACC) and radar brake systems.

The radar apparatus revealed in U.S. Pat. No. 5,486,832 continuouslyradiates from a transmit antenna a broad fixed beam forwardly of themotor vehicle which carries the radar apparatus, and switches aplurality of receive antenna elements sequentially to receive areflected beam. According the disclosure, the transmitted beam is notscanned, but the receive antenna elements are sequentially switched toreceive the reflected beam for thereby monitoring an obstaclehorizontally ahead of the motor vehicle. One drawback of the disclosedradar apparatus is that the transmit antenna and the receive antennaelements are located in separate positions. A dielectric lens used bythe radar apparatus for converging a high-frequency beam is generallycostly to manufacture. The cost of the radar apparatus will be high ifindependent lenses are used to transmit and receive a high-frequencybeam.

Radar systems for motor vehicles are mostly mounted on front bumpers,and hence should be small in size. In addition, the radar systems formotor vehicles are required to have an increased azimuth resolution. Ifthe width of the high-frequency beam is reduced to increase the azimuthresolution, then the dielectric lens has to have an increased diameter.According to the radar apparatus disclosed in U.S. Pat. No. 5,486,832,the entire antenna assembly is large because the transmit antenna andthe receive antenna elements are fully independent of each other. Thehigher the azimuth resolution, the greater the antenna assembly, makingit more difficult to install the radar apparatus on front bumpers.

It is preferable to reduce the width of the beam radiated from thetransmit antenna for the purpose of minimizing interferences betweenradar apparatus on motor vehicles. However, the radar apparatusdisclosed in U.S. Pat. No. 5,486,832 is susceptible to suchinterferences because a broad fixed beam is continuously radiated fromthe transmit antenna.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a multibeam radarsystem which has an inexpensive scanning arrangement for scanning ahigh-frequency beam.

Another object of the present invention is to provide a multibeam radarsystem which has a single dielectric lens or parabolic reflecting mirrorfor ease of installation on motor vehicles and a low cost.

Still another object of the present invention is to provide a multibeamradar system which has an increased number of azimuth channels for anincreased azimuth resolution while minimizing interferences betweentransmitting and receiving antenna elements.

A yet still another object of the present invention is to provide amultibeam radar system which transmits and receives FM signals in atime-sharing fashion to reduce interferences between radar systems onmotor vehicles.

According to an aspect of the present invention, there is provided amultibeam radar antenna comprising a dielectric substrate and aplurality of transmitting/receiving channels for transmittinghigh-frequency signals and receiving echo signals, thetransmitting/receiving channels being mounted on the dielectricsubstrate and comprising a first group of planar array antenna elementsas a transmitting primary radiator and a second group of planar arrayantenna elements as a receiving primary radiator, the first group ofplanar array antenna elements and the second group of planar arrayantenna elements being disposed in opposite relation to each other onthe dielectric substrate.

The first group of planar array antenna elements and the second group ofplanar array antenna elements are disposed in interdigitating relationto each other on the dielectric substrate. The multibeam radar antennamay further include a electromagnetic shield partition disposed on thedielectric substrate, the first group of planar array antenna elementsand the second group of planar array antenna elements being separatedfrom each other by the electromagnetic shield partition disposedtherebetween.

According to another aspect of the present invention, there is provideda multibeam radar module comprising a dielectric substrate and aplurality of transmitting/ receiving channels for transmittinghigh-frequency signals and receiving echo signals, thetransmitting/receiving channels being mounted on the dielectricsubstrate and comprising a first group of planar array antenna elementsas a transmitting primary radiator and a second group of planar arrayantenna elements as a receiving primary radiator, the first group ofplaner array antenna elements and the second group of planar arrayantenna elements being disposed in opposite relation to each other onthe dielectric substrate, and a plurality of switching devices mountedon the dielectric substrate for selectively operating thetransmitting/receiving channels to transmit the high-frequency signalsand receive the echo signals.

The plurality of transmitting/receiving channels may comprise n (n is anatural number of at least 3) transmitting/receiving channels, and achannel controller may control the switching devices to select sets of m(m is a natural number smaller than n) adjacent transmitting/receivingchannels sequentially to transmit the high-frequency signals and receivethe echo signals. Alternatively, the channel controller may control theswitching devices to select the transmitting/receiving channelssequentially one by one.

The high-frequency signals and the echo signals may comprise FM signalswhose frequencies are variable with time, and a mixer may mix thetranmitted high-frequency signals and the echo signals to generate beatsignals.

According to still another aspect of the present invention, there isprovided a multibeam radar system comprising a multibeam radar modulehaving n (n is a natural number of at least 3) transmitting/receivingchannels for transmitting high-frequency signals and receiving echosignals, and a radar circuit for detecting a distance up to an objectwhich produces the echo signals and/or a relative speed of the objectfrom a relationship between the high-frequency signals and the echosignals in the transmitting/receiving channels, the radar circuitincluding a channel controller for selecting sets of m (m is a naturalnumber smaller than n) adjacent transmitting/receiving channelssequentially to transmit the high-frequency signals and receive the echosignals.

According to yet still another aspect of the present invention, there isprovided a multibeam radar system comprising a multibeam radar modulehaving a plurality of transmitting/receiving channels for transmittinghigh-frequency signals and receiving echo signals, and a radar circuitfor detecting a distance up to an object which produces the echo signalsand/or a relative speed of the object from a relationship between thehigh-frequency signals and the echo signals in thetransmitting/receiving channels, the radar circuit including a channelcontroller for selecting the transmitting/receiving channelssequentially one by one to transmit the high-frequency signals andreceive the echo signals.

According to a further aspect of the present invention, there isprovided a multibeam radar system comprising a multibeam radar modulehaving n (n is a natural number of at least 3) transmitting/receivingchannels for transmitting high-frequency signals and receiving echosignals, and a radar circuit for detecting a distance up to an objectwhich produces the echo signals and/or a relative speed of the objectfrom a relationship between the high-frequency signals and the echosignals in the transmitting/receiving channels, the radar circuitincluding a channel controller for alternatively selecting sets of m (mis a natural number smaller than n) adjacent transmitting/receivingchannels sequentially to transmit the high-frequency signals and receivethe echo signals in a high-azimuth-resolution mode and selecting thetransmitting/receiving channels sequentially one by one to transmit thehigh-frequency signals and receive the echo signals in alow-azimuth-resolution mode.

The channel controller may select the high-azimuth-resolution mode andthe low-azimuth-resolution mode alternatively depending on a range to bedetected by the radar circuit. The channel controller may select thehigh-azimuth-resolution mode and the low-azimuth-resolution modealternately in predetermined periodic cycles.

The above and other objects, features, and advantages of the presentinvention will become apparent from the following description when takenin conjunction with the accompanying drawings which illustrate preferredembodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a physical structure of a multibeam FM radarmodule according to an embodiment of the present invention;

FIG. 2 is a block diagram of a multibeam FM radar system whichincorporates the multibeam FM radar module shown in FIG. 1;

FIG. 3 is a perspective view of a substantially parabolic reflectingmirror combined with the multibeam FM radar module shown in FIG. 1;

FIG. 4 is a perspective view of a dielectric lens combined with themultibeam FM radar module shown in FIG. 1;

FIG. 5 is a diagram showing vertical and horizontal radiation patternsof a three-element patch array antenna;

FIG. 6 is a timing chart illustrative of the manner in which sets ofthree adjacent transmitting/receiving channels are operatedsequentially;

FIG. 7 is a diagram showing vertical and horizontal radiation patternsof a one-element patch array antenna;

FIG. 8 is a timing chart illustrative of the manner in whichtransmitting/receiving channels are operated sequentially one by one;

FIG. 9 is a diagram illustrative of a horizontal radiation pattern in ahigh-azimuth-resolution mode and a horizontal radiation pattern in alow-azimuth-resolution mode;

FIG. 10 is a plan view of a physical structure of a multibeam FM radarantenna according to another embodiment of the present invention; and

FIG. 11 is a block diagram of a multibeam FM radar system whichincorporates the multibeam FM radar antenna shown in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a multibeam FM radar module 10 according to an embodimentof the present invention, and FIG. 2 shows a multibeam FM radar systemwhich incorporates the multibeam FM radar module 10 shown in FIG. 1.

As shown in FIG. 1, the multibeam FM radar module 10 comprises atransmitting primary radiator which comprises a plurality of (eight)planar patch array antenna elements 12a, 12b, 12c, . . . , 12h in theform of microstrips and a receiving primary radiator which comprises aplurality of (eight) planar patch array antenna elements 13a, 13b, 13c,. . . , 13h in the form of microstrips. The patch array antenna elements12a, 12b, 12c, . . . , 12h and the patch array antenna elements 13a,13b, 13c, . . . , 13h jointly provide respective transmitting/receivingchannels. The patch array antenna elements 12a, 12b, 12c, . . . , 12hand the patch array antenna elements 13a, 13b, 13c, . . . , 13h aremounted in opposite interdigitating relation to each other on adielectric substrate 11. The multibeam FM radar module also comprises aplurality of switching devices 14a, 14b, 14c, . . . , 14h mounted on thedielectric substrate 11 and electrically connected respectively to thepatch array antenna elements 12a, 12b, 12c, . . . , 12h, and a pluralityof switching devices 15a, 15b, 15c, . . . , 15h mounted on thedielectric substrate 11 and electrically connected respectively to thepatch array antenna elements 13a, 13b, 13c, . . . , 13h. Each of theswitching devices 14a, 14b, 14c, . . . , 14h and the switching devices15a, 15b, 15c, . . . , 15h comprises an MMIC (Monolithic MicrowaveIntegrated Circuit) which includes high electron mobility transistors(HEMT). However, each of the switching devices 14a, 14b, 14c, . . . ,14h and the switching devices 15a, 15b, 15c, . . . , 15h may comprisepin diodes instead of an MMIC of HEMTs.

As shown in FIG. 2, the patch array antenna elements 12a, 12b, 12c, . .. , 12h are electrically connected through the respective switchingdevices 14a, 14b, 14c, . . . , 14h and a common feed line 19 to an FMsignal generator 23 of a main radar circuit 20. The patch array antennaelements 13a, 13b, 13c, . . . , 13h are electrically connected throughthe respective switching devices 15a, 15b, 15c, . . . , 15h and a commonfeed line to an input terminal of a mixer 16 which is mounted on thedielectric substrate 11. Another input terminal of the mixer 16 isconnected to the FM signal generator 23 through the feed line 19. Themixer 16 may be not only single mixer but also a plurarity of mixerscorrespond to the each switchng device 15a, 15b, 15c, . . . , 15h andthe each patch array antenna elements 13a, 13b, 13c, . . . , 13h.

The transmitting and receiving primary radiators are used as a primaryradiator of an offset defocused multiple-beam parabolic antenna shown inFIG. 3. As shown in FIG. 3, the multibeam FM radar module 10 is mountedon a holder 40 and positioned in the vicinity of the focal point of asubstantially porabolic reflecting surface 30, serving as a secondaryradiator, which is coupled to the holder 40 and faces the holder 40.

The transmitting and receiving primary radiators and the substantiallyparabolic reflecting surface 30 as the secondary radiator jointly makeup the offset defocused multiple-beam parabolic antenna. The offsetdefocused multiple-beam parabolic antenna is typically mounted on thefront bumper of a motor vehicle.

The substantially porabolic reflecting surface 30 may be replaced withanother reflecting surface such as a cylindrical reflecting surface, ahyperbolic reflecting surface, a horn-shaped reflector, or a cornerreflector.

The multibeam FM radar module shown in FIG. 1 may instead be combinedwith a dielectric lens 50 as shown in FIG. 4. In FIG. 4, the multibeamFM radar module is positioned in the vicinity of the focal point of thedielectric lens 50.

As shown in FIG. 2, an FM signal generated by the FM signal generator 23is supplied through the switching devices 14a, 14b, 14c, . . . , 14h tothe patch array antenna elements 12a, 12b, 12c, . . . , 12h, whichradiate FM signal beams. The FM signal from the FM signal generator 23is also supplied to the mixer 16. The radiated FM signal beams arereflected by the reflecting surface 30, and radiated in slightlydifferent directions, respectively, from the reflecting surface 30 withadjacent ones of the radiated FM signal beams overlapping each other.When the radiated FM signal beams are reflected as echo FM signal beamsby an object such as another motor vehicle, the echo FM signal beamstravel back to the reflecting surface 30 and reflected thereby to thepatch array antenna elements 13a, 13b, 13c, . . . , 13h. The receivedecho FM signals are selected by the switching devices 15a, 15b, 15c, . .. , 15h and supplied to the mixer 16.

The mixer 16 generates a beat signal by mixing the FM signal from the FMsignal generator 23 and the echo FM signals from the switching devices15a, 15b, 15c, . . . , 15h. The beat signal is supplied to the mainradar circuit 20. In the main radar circuit 20, the beat signal issupplied through a switching device 24 to an A/D (analog-to-digital)converter 25, which converts the analog beat signal to a digital signal.The digital signal is supplied to a fast-Fourier transform (FFT) circuit26. The fast-Fourier transform circuit 26 effects a fast-Fouriertransform on the digital beat signal to generate a frequency spectrumsignal of the beam signal, and sends the frequency spectrum signal to aCPU (central processing unit) 21. The CPU 21 detects a beat frequencyfrom the frequency spectrum signal, and determines the distance up tothe object which has reflected the FM signal beams and a rate of changeof the distance with respect to time based on the detected beatfrequency. The CPU 21 stores data about the determined distance and rateof change thereof in a memory 27.

At the same time, the CPU 21 controls a channel controller 22 to selectthe transmitting/receiving channels successively for transmitting FMsignal beams and receiving echo FM signal beams. Specifically, thechannel controller 22 sends control signals to the switching devices14a, 14b, 14c, . . . , 14h and the switching devices 15a, 15b, 15c, . .. , 15h for selecting the transmitting/receiving channels sequentiallyin sets of adjacent channels or one by one.

For example, if three adjacent transmitting/receiving channels aresimultaneously selected, vertical and horizontal radiation patterns ofthree patch array antenna elements, i.e., a three-element patch arrayantenna, are similarly sharp as shown in FIG. 5.

In such a three-element selection mode, control signals supplied fromthe channel controller 22 to the switching devices 14a˜14h, 15a˜15h areturned on and off as shown in FIG. 6. In FIG. 6, the control signals asthey are turned on represent activation of the channels A˜H, and thecontrol signals as they are turned off represent inactivation of thechannels A˜H. When the control signals are turned on as shown in FIG. 6,sets of three channels A, B, C, three channels B, C, D, three channelsC, D, E, and so on are selected sequentially to transmit and receive FMsignal beams. In this three-element selection mode, the horizontalradiation pattern is also sharp for detecting an object in a far rangewith a high azimuth resolution.

If one of the transmitting/receiving channels is selected at a time,then a horizontal radiation pattern of one patch array antenna element,i.e., a one-element patch array antenna, is wider than its verticalradiation pattern as shown in FIG. 7.

In such a one-element selection mode, control signals supplied from thechannel controller 22 to the switching devices 14a˜14h, 15a˜15h areturned on and off as shown in FIG. 8. In FIG. 8, the control signals asthey are turned on represent activation of the channels A˜H, and thecontrol signals as they are turned off represent inactivation of thechannels A˜H. When the control signals are turned on as shown in FIG. 8,the channels A˜H are selected sequentially one by one to transmit andreceive FM signal beams. In this one-element selection mode, thehorizontal radiation pattern is wider than the vertical radiationpattern for detecting an object in a short wide range near the motorvehicle.

FIG. 9 shows a horizontal radiation pattern in a high-azimuth-resolutionmode, which may be the three-element selection mode, and a horizontalradiation pattern in a low-azimuth-resolution mode, which may be theone-element selection mode. In the high-azimuth-resolution mode, sharpFM signal beams are radiated from the multibeam radar antenna to a fararea in front of the motor vehicle. In the low-azimuth-resolution mode,short wide FM signal beams are radiated from the multibeam radar antennato a near wide area in front of the motor vehicle.

According to a modification, the CPU 21 may control the channelcontroller 22 to select the transmitting/receiving channels in a mannerto operate alternately in the high-azimuth-resolution mode and thelow-azimuth-resolution mode in predetermined periodic cycles for therebymonitoring the far area and the near wide area alternately.Alternatively, the CPU 21 may control the channel controller 22 toselect sets of two adjacent channels, i.e., two channels A, B, twochannels B, C, two channels C, D, and so on (see FIG. 6) sequentially totransmit and receive FM signal beams for thereby achieving a resolutionintermediate between the resolutions of the modes shown in FIGS. 6 and8, respectively. Further alternatively, the CPU 21 may control thechannel controller 22 to select sets of four adjacent channels, i.e.,four channels A, B, C, D, four channels B, C, D, E, four channels C, D,E, F, and so on (see FIG. 6) sequentially to transmit and receive FMsignal beams for thereby achieving a resolution higher than theresolution of the mode shown in FIG. 6.

FIG. 10 shows a physical structure of a multibeam FM radar antennaaccording to another embodiment of the present invention, and FIG. 11shows a multibeam FM radar system which incorporates the multibeam FMradar antenna shown in FIG. 10.

In FIG. 10, the multibeam FM radar antenna comprises a plurality of(sixteen) patch array antenna elements 12a, 12b, 12c, . . . , 12p in theform of microstrips and a receiving primary radiator which comprises aplurality of (sixteen) patch array antenna elements 13a, 13b, 13c, . . ., 13p in the form of microstrips. The patch array antenna elements12a˜12p and the patch array antenna elements 13a˜13h are mounted inopposite relation to each other on a dielectric substrate 11, andseparated from each other by a electromagnetic shield partition 9disposed therebetween centrally on the dielectric substrate 11.

In FIG. 11, those parts which are identical to those shown in FIG. 2 aredesignated by identical reference numerals and representations, and willnot be described in detail below. The multibeam FM radar antennaincludes a plurality of mixers 16a˜16p associated respectively with thesixteen transmitting/receiving channels, and a plurality oflocal-oscillation switching devices 17a˜17p for selectively supplyinglocal oscillation signals to the mixers 16a˜16p, respectively. Beatsignals generated by the respective mixers 16a˜16p are amplified byrespective intermediate-frequency amplifiers Aa˜Ap and then supplied toa selector 28 of the main radar circuit 20.

The multibeam FM radar system shown in FIG. 11 operates essentially inthe same manner as the multibeam FM radar system shown in FIG. 2.

The principles of the present invention are also applicable to multibeamradar modules or systems of other types including a multibeam AM radarmodule or multibeam pulse doppler radar system.

With the arrangement of the present invention, as described above, sincethe transmitting primary radiator comprising patch array antennaelements and the receiving primary radiator comprising patch arrayantenna elements are separate from each other, no circulators arerequired by the multibeam radar module and the multibeam radar antenna.Therefore, the multibeam radar module and the multibeam radar antennamay be relatively small in size.

The patch array antenna elements of the transmitting primary radiatorand the patch array antenna elements of receiving primary radiator aremounted in opposite relation on the single dielectric substrate.Therefore, any interferences between adjacent ones of thetransmitting/receiving channels are minimized for increased detectionaccuracy. The antenna of the present invention may be used in indoorcommunication sysytem.

The transmitting/receiving channels are selected sequentially in sets ofadjacent channels or one by one. Consequently, the multibeam radarmodule and the multibeam radar antenna provides high azimuth detectionaccuracy.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

What is claimed is:
 1. A multibeam radar module comprising:a dielectricsubstrate; and a plurality of transmitting/receiving channels fortransmitting high-frequency signals and receiving echo signals, saidtransmitting/receiving channels being mounted on said dielectricsubstrate and comprising a first group of planar array antenna elementsas a transmitting only primary radiator and a second group of planararray antenna elements as a receiving only primary radiator, said firstgroup of planar array antenna elements and said second group of planararray antenna elements being disposed in interdigitating relation toeach other on said dielectric substrate to reduce interference betweenthe first and second groups of antenna elements; and a plurality ofswitching devices mounted on said dielectric substrate for selectivelyoperating said transmitting/receiving channels to transmit saidhigh-frequency signals and receive said echo signals.
 2. A multibeamradar module according to claim 1, wherein said plurality oftransmitting/receiving channels comprise n (n is a natural number of atleast 3) transmitting/receiving channels, further comprising a channelcontroller for controlling said switching devices to select sets of m (mis a natural number smaller than n) adjacent transmitting/receivingchannels sequentially to transmit said high-frequency signals andreceive said echo signals.
 3. A multibeam radar module according toclaim 1, further comprising a channel controller for controlling saidswitching devices to select said transmitting/receiving channelssequentially one by one.
 4. A multibeam radar module according to claim1, wherein said high-frequency signals and said echo signals comprise FMsignals whose frequencies are variable with time, further comprising amixer for mixing said high-frequency signals and said echo signals togenerate beat signals.
 5. A multibeam radar system comprising:amultibeam radar module having n (n is a natural number of at least 3)transmitting/receiving channels for transmitting high-frequency signalsand receiving echo signals; and a radar circuit for detecting a distanceup to an object which produces said echo signals and/or a relative speedof said object from a relationship between said high-frequency signalsand said echo signals in said transmitting/receiving channels, saidradar circuit including a channel controller for selecting sets of m (mis a natural number smaller than n) transmitting receiving channels,having separate transmit only and receive only antennas, sequentially totransmit said high-frequency signals and receive said echo signals.
 6. Amultibeam radar system comprising:a multibeam radar module having n (nis a natural number of at least 3) transmitting/receiving channels fortransmitting high-frequency signals and receiving echo signals; and aradar circuit for detecting a distance up to an object which producessaid echo signals and/or a relative speed of said object from arelationship between said high-frequency signals and said echo signalsin said transmitting/receiving channels, said radar circuit including achannel controller for alternatively selecting sets of m (m is a naturalnumber smaller than n) transmitting/receiving channels sequentially totransmit said high-frequency signals and receive said echo signals in ahigh-azimuth-resolution mode and selecting said transmitting receivingchannels, having separate transmit only and receive only antennas,sequentially one by one to transmit said high-frequency signals andreceive said echo signals in a low-azimuth-resolution mode.
 7. Amultibeam radar system according to claim 6, wherein said channelcontroller selects said high-azimuth-resolution mode and saidlow-azimuth-resolution mode alternatively depending on a range to bedetected by said radar circuit.
 8. A multibeam radar system according toclaim 6, wherein said channel controller selects saidhigh-azimuth-resolution mode and said low-azimuth-resolution modealternately in predetermined periodic cycles.
 9. A multibeam radarsystem according to claim 6, wherein said high-frequency signals andsaid echo signals comprise FM signals whose frequencies are variablewith time.
 10. A multibeam radar system according to claim 9, whereinsaid radar circuit further comprises a mixer for mixing saidhigh-frequency signals and said echo signals to generate beat signals.